It is well known that self-supporting films formed of synthetic linear polyesters, particularly the polyesters formed by the reaction of ethylene glycol with therephthalic acid, may be prepared in such a manner that they have mechanical and physical and chemical properties which render them highly suitable for use as base materials or substrate materials on which can be coated silver halide photographic emulsions.
A large number of self-supporting film materials are known as supporting substrates for photographic film. Generally, such materials are essentially hydrophobic in character and many are highly hydrophobic. Considerable difficulty is often encountered in providing adequate adhesion of the hydrophilic emulsion to the hydrophobic substrate. Strong adhesion is absolutely necessary in view of the physical and chemical processing to which the photographic film is subjected.
In order to provide adequate adhesion of a hydrophilic layer, such as a gelatin silver halide emulsion to a polyester film, it is known to provide intermediate layers of varying hydrophilicity between the substrate and the photographic emulsion. In many cases, a plurality of intermediate layers are employed. A first layer, generally characterized by good adhesion to the polyester film, is frequently referred to as the priming layer. A second layer, called a subbing layer and usually containing a substantial amount of a hydrophilic collodial material, such as gelatin, is coated onto the priming layer. The photographic emulsion layer is then coated on the subbing layer. It is generally believed, and therefore the practice in the industry, that good adhesion of the photographic emulsion layer to the hydrophobic film surface can only be obtained when the surface of the hydrophobic material has been properly primed and subbed with an intermediate layer or layers containing a sufficient amount of a hydrophilic material.
It is an object of this invention to provide methods and materials for improving the adhesion of a gelatin-containing photographic emulsion to a hydrophobic film base or substrate, particularly to polyester substrates.
Another object of the invention is to provide photographic elements having a gelatin-containing silver halide emulsion which elements are characterized by improved adhesion of the emulsion to the film base.
A further object of the invention is to provide photographic elements having a hydrophobic film base and a hydrophilic photographic emulsion characterized by improved adhesion without need for conventional priming and subbing layers having varying degrees of hydrophobicity.
A more specific object being to eliminate the need for intermediate subbing layers containing gelatin as a hydrophilic material.